This invention relates to turbomachinery and, more particularly, to a method for detecting and quantifying combustor dynamic pressures.
Excessive dynamic pressures (or dynamics) within Dry Low NOx (DLN) combustion systems must be avoided in order to assure acceptable system durability and reliability. As DLN combustion systems become more aggressive with regard to emissions and gas turbine cycles, the combustors tend to become less robust against these combustor dynamic pressure fluctuations (dynamics), and system failures caused by excessive dynamics are possible. In some cases, continuous monitoring of combustor dynamics with internally mounted dynamic pressure transducers is required as an instantaneous warning system. Dynamic pressure transducers are expensive, however, and require continuous maintenance monitoring. Additionally, since dynamic pressure transducers are mounted internally of the pressure vessels, replacement of the transducers requires shutdown and subsequent cooling of the machine.
This invention provides a method of detecting combustor dynamic pressures from outside of the pressure vessel, so that continuous operation of a gas turbine is not effected by instrumentation related problems, maintenance or other concerns.
In an exemplary embodiment, an accelerometer is mounted externally on each combustor casing and measures a vibration signature for that casing, and thus detects and quantifies combustor dynamic pressures for that specific combustor. The advantages of this technique include: (a) all instrumentation is mounted external to the pressure vessel, allowing online maintenance without a turbine shutdown; (b) the long term reliability of accelerometers leads to a permanent dynamics pressure measurement system; and (c) it is less expensive than currently used PCB probes mounted internally of the combustor casing.
In order to implement the method, it is required that a baseline combustor case vibration signature be recorded for comparison purposes. Thus, a vibration signature is recorded when it is known that combustor dynamics are minimal, such as during a diffusion flame mode. By continuously measuring subsequent vibration signatures through all load ranges, and comparing them to the baseline, the onset of excessive combustor dynamics can be detected.
Accordingly, in its broader aspects, the present invention relates to a method of detecting combustor dynamic pressures in combustors of a gas turbine combustor comprising: a) mounting at least one accelerometer on a combustor casing; b) establishing a baseline vibration signature for the casing when combustion dynamics are minimal; c) measuring subsequent vibration signatures for the casing and comparing those signatures.